Traumatic brain injury (TBI) is a significant health care issue in the United States affecting more than 2 million persons annually, with approximately 500,000 hospital admissions. Rapid and sustained calpain activation is thought to be an important intracellular event mediating the neuropathological response to TBI. In addition, the interleukin- 1beta-converting enzyme (ICE) family of cysteine proteases (recently renamed caspases) has also been posited as having an important role in the pathophysiology of TBI. However, regional and temporal profiles of these proteases in TBI have not been fully characterized. The Specific Aims of this proposal are to examine calpain-and caspase-mediated proteolysis of the neuronal cytoskeletal protein, alpha-spectrin, in various brain regions from 15 minutes to 90 days following rodent TBI, and to correlate the profile of spectrin degradation to neuromorphological alterations. A novel feature of this project is the employment of an antibody that concurrently immunolabels native alpha- spectrin (240 kD), the calpain-specific spectrin breakdown product (SBDP) (145 kD), and the caspase-specific SBDP (120 kD) on Western blots. The Specific Aims are focused towards addressing the central hypothesis that TBI causes rapid and enduring regionally- and temporally-specific patterns of calpain- and caspase-mediated alpha- spectrin proteolysis in brain regions known to be vulnerable to neuronal insult. This investigation will contribute to the growing body of knowledge regarding the pathophysiological mechanisms contributing to cellular, parenchymal, and behavioral morbidity following TBI.